Metal matrix composites (sometimes referred to as MMC's) are finding increasingly widespread application in many fields of industry by virtue of the desirable manner in which the properties of such composites can be selectively engineered. These types of composites often comprise a non-metallic porous core, such as comprising ceramic materials, and metallic material which is introduced in a molten state to infiltrate the porous core. The core material may be provided in differing forms, such as particles or fibers, and may comprise up to 80%, or more, of the volume of the resultant composite.
Selection of the specific core materials, as well as the infiltrating metal, permits the physical and mechanical properties of the resultant composite to be selectively engineered. For example, such composites can be engineered to provide desirably high strength-to-weight ratios. A particularly advantageous use of such engineered composites is for mounting and packaging of electronic components, such as integrated circuitry. By appropriate selection of the core material and associated metal, composites exhibiting desirably high coefficients of heat transfer, with desirably low coefficients of thermal expansion, can be readily fabricated.
U.S. Pat. No. 5,259,436, to Yun et al., discloses highly effective techniques for efficient manufacture of metal matrix composites, which can typically be formed with silicon carbide cores infiltrated with molten aluminum or aluminum alloys. A wide variety of core materials, as well as associated infiltrating metallic materials, can be employed in accordance with the teachings of this patent.
In accordance with the teachings of the above-referenced patent, one particularly preferred technique for effecting metal matrix composite manufacture entails preparation of a preform of the material which forms the porous core of the composite, and preheating of the preform prior to its disposition in an associated die caster for infiltration with pressurized molten metal. This formation technique permits the porous core of the composite to be precisely engineered for optimizing the desired physical characteristics of the resultant composite, while at the same time ensuring the structural integrity of the preform during pressurized metal infiltration.
In a particularly preferred technique, a preform is manufactured from particles of silicon carbide, which particles are preferably selected from a plurality of size ranges so that the small particles fill the interstices defined by larger ones of the particles. During blending of the particles, binder materials can be introduced to facilitate shaping of the preform. Heating of this preform is preferably effected to at least partially sinter the particles, and to volatize and drive off any binder materials which may have been applied to the particles. Partial sintering of the preform maintains the desired level of porosity of the composite core, while integrating the particles into a shaped form which can be matched to that of the resultant composite, as desired. The preform typically exhibits sufficient structural integrity to promote its handling, including subsequent disposition in the die caster, without undesired chipping, disintegration, or other damage.
In accordance with the above-referenced patent, infiltration of the preform with molten metal is preferably enhanced by preheating the preform to a temperature at or above the temperature of the molten metal with which the preform is infiltrated. Because this preheating can be effected exteriorly of the die caster, heating of the preform to a temperature greater than that of the molten metal allows for the inevitable cooling that takes place as the preform is moved from the preheating apparatus into the die caster. It is desired that the preform be at a temperature at or above the temperature of the molten metal to promote metal infiltration, and to avoid cooling of the molten metal by the preform prior to substantially complete infiltration. The above patent also contemplates that infiltration can be further enhanced by substantially evacuating the die cavity of the die caster, within which the preform is positioned, thus also evacuating the porous structure of the preform.
The above-referenced U.S. Pat. No. 5,259,436 is hereby incorporated by reference.
The present invention is directed to a system for promoting efficient manufacture of metal matrix composites, with a system including an automated, programmable arrangement for efficiently and sequentially handling porous preforms for preheating, and subsequent positioning in the die cavity of a die caster for molten metal infiltration.